The Door into Summer is a science fiction novel by American science fiction writer Robert A. Heinlein, originally serialized in The Magazine of Fantasy & Science Fiction. It was published in hardcover in 1957.

The Door into Summer is a 2021 Japanese science fiction film directed by Takahiro Miki and starring Kento Yamazaki, Kaya Kiyohara, Naohito Fujiki, Natsuna, and Hidekazu Mashima. Based on Robert A. Heinlein's novel of the same name, it was released on June 25, 2021.